So I figured it really can't be neither a VRAM issue or SLI issue last night, when I was trying MP..
Again, setup is i5 @ 4Ghz, 2x GTX 460 1GB SLI (OC'd, 850 core/2000 mem), 4Gb 1600Mhz RAM and latest nVidia drivers.
I could play on 1080p Ultra (though 2xAA/Medium Post AA/SSAO) with SLI enabled for a while, then I get MASSIVE unplayable stuttering, freezeframed for like 3 seconds at a time.
Tried again on another server/map - could play for about 15 minutes to the end of the match quite problem free, some drops here and there.
Next map, played for about 10 minutes, then the bad drops started again, so I quit.
Next time, new map and server, but this time lowered the settings to 1680x1050, High instead of Ultra on all settings, and 8x Anisotropic filtering, my setup should handle this just fine. Did it work? Nope, still unplayable after a little while.
Next test, disable SLI. same settings as above. Was telling myself it was a bit better, but the stuttering came anyway, just that it may have taken a bit longer to happen, but all my tests have been on different maps, so it's still not conclusive to anything.
I'm thinking there's something very wrong with the drivers or the game..